Supercharger For Extracting Exhaust Gas.

[Rolls]

Instead of a supercharger supercharging the air going into an engine what about sucking the exhaust out of an engine. You would put this post turbo on a turbocharged car as these are the type of engine that would greatly benefit from lower back pressure.

Has this ever been done, would it be effective?

Discuss.

Edited September 5, 2011 by Rolls

[Tangles]

You could use a cheap 'smog pump' from a US wrecker as in essence it works like a supercharger on the exhaust gases. Would have liked to hook one up to my old motorbike intake, run off a airconditioner pulley motor. Could use this theory to help evacuate exhaust gasses quickly as per your thoughts. Wouldn't cost much to fabricate & try out.

[SargeRX8]

I can't imagine the pipe work. If its electrical it would be hard to setup and it is going to have to be designed VERY well and suited to each engine. Too many factors. The more boost you run means more fuel means bigger combustion means more exhaust, what if this thing can't suck the exhaust as fast as the engine is shitting it out? It would end up being a restriction. What if it spins too fast and creates a vortex of turbulence against the exhaust wheel of the turbo... Or maybe it can assist in spinning the exhaust wheel and creating faster spool time.

[Room42]

Lol when I was just a kid of 9 years old I heard the term extractor. Your idea is what I thought it was. I've never thought about it since. Sounds alright tho as long as it is regulated...

[Legionnaire]

Interesting suggestion, but what's the idea behind this? Improvment of pressure differential across turbine stage of a turbo? It may benefit turbo itself, e.g. make it spool faster and use much smaller wastegates, but I can't see it adding any power to the engine?

[karma_syke]

i don't think this would work or have any kind of benefit at all. The turbine on the turbo uses the 'free' or unused energy that the fast moving exhaust gasses produce to in turn feed more air back in. I don't see any net advantage to use energy derived from the crankshaft to help spool a (turbo) - might as well be a supercharger from the beginning.

edit: before the so called experts see this thread and try to flame the OP for even suggesting it ("nissan spend millions in R&D and if it was such a good idea they would have done it before u so stupid") - lay off him, he's just having a crack and there's no harm in it. If you feel so strongly about it politely post the physics based reasons why may/may not work.

Edited September 5, 2011 by karma_syke

[bigmikespec]

Just build a twin charged engine and you will get higher boost pressure to turbine back pressure anyway... done!

[The Mafia]

lol.

I can't believe some of the questions that get asked here, and then we get told not to flame.

Ok, I'll make up some good ideas on the spot:

1. Why don't they just make pistons out of titanium?

2. Umm, why can't we just make a way to burn water instead of fuel? Its cheaper?

3. Why don't we replace spark plugs with plasma torches? You'd get better ignition?

4. To save problems with gearboxes, I'm going to try and just take away the gearbox, and make my engine rev higher, to say, 30,000rpm. Then we won't have to worry about breaking the gearbox?

5. Why aren't superchargers just electric? Thats easier right?

oh, and look what I did to my turbo to make it better:

"nissan spend millions in R&D and if it was such a good idea they would have done it before"

[R31Nismoid]

Rolls what kinda drugs do you take man, i need some

Rememember a supercharger = infront of the heat, not behind it. That is going to be the typical enemy.

All a supercharger does is pressurise the intake, same as a turbo. Its just doing it mechanically rather than turbine based.

Superchargers given mechanically driven = off the motor. How do you intend to get the belts behind the exhaust manifold area?

[Legionnaire]

I think he just meant a pump, roots-style, with no internal compression, that would suck gasses out of the engine. Why would that be needed is a totally different question.

[sneakey pete]

Your just doing the work twice with that setup aren't you? i mean the piston itself pushing up on the exhaust stroke is just a big pump pumping the gasses out of the chamber.

[karma_syke]

At least i tried.

...lol

[tridentt150v]

In theory you would have to have the 'pump' very close to the turbo/dump area. As the exhaust gases rush out they rapidly cool so by the time you get past the cat and to the back part of the exhaust system [unless you have very restrictive mufflers] their is a heaps of 'extra' room and even some negative pressure.

Your dump is 90mm, your exhaust is 90mm and the air is cooling and contracting = the largest pressure is at the turbo exit.

But tbh, I think any mechanical advantage would be beaten by the turbulence created by the pump.

[SargeRX8]

1. Why don't they just make pistons out of titanium?

3. Why don't we replace spark plugs with plasma torches? You'd get better ignition?

"nissan spend millions in R&D and if it was such a good idea they would have done it before"

You might be onto something here

Nissan did spend alot of money but there are certainly things they could have done better... Do you think they tried and tested the RB as a non interference motor?

[hypergear]

The engine need inlet manifold boost pressure to carry out the more air burn more fuel = more energy theory. By charging the exhaust it can virtually lower exhaust pressure after the turbo.

Ie. I run 24psi out of my pretty quite exhaust and I have 6psi in my exhaust by 7000RPMs, Using a very powerful exhaust charger I can get it down to maybe 1~2 psi, might alter tinny bit on the dyno reading up top. How ever running it along would give similar effect as a big exhaust perhaps.

Also to get a electric charger powerful enough to produce or suck 6psi you are going to need a 8.4HP electric unit, run that into a 12V setup the current draw is about 600amps? (not exactly sure). Might require less as the dispatching requires less energy then compressing.

Try it out and prove it works or not.

[Birds]

Whatever benefit it gives, would be removed by the energy consumption IMO.

Consider that the principles behind supercharger and turbocharger are forcing more air and fuel into the engine for the purposes of greater combustion forces upon the pistons, in an atmosphere where ordinarily the amount of air and fuel intake is limited to the vacuum and capacity of the engine. It doesn't really work the other way, when you have no combustion for exhaust gas stroke - all you are doing is extracting exhaust from the cylinders, which the engine has no trouble doing, given exhaust valves open as soon as the exhaust stroke begins.

As for spooling up a turbocharger faster / pre-spooling it...could work with properly designed plumbing...but I doubt the benefit/consumption equation would work out. Consider how much air is being pushed out by the engine at 2000rpm to start spooling a standard Skyline turbo...your supercharger would need to pull that much out to make it worthwhile = fair bit of power to turn it that quickly.

As for solving back pressure issues, well you can run a 5 inch pipe and end up with zero...

The only advantage I could see to this, if the theory could be applied, is that you could have variable backpressure with controlled extraction of the exhaust gases via different operating speeds of the supercharger. Again, whether the benefits outweigh the effort or energy put into it, is another thing.

Better off focusing on a way to use unburnt fuel in the exhaust gases to further power the vehicle

[tridentt150v]

No No No what you really need is a nozzle on the exhaust, this way you will get a huge forward thrust from the exhaust gases being blasted out like a jetstream. Then you would need a dual exhaust system to balance the power otherwise you would end up spinning out of control!!!

[FineLine]

WANTED....Small black man to work as mudflap, Must be flexible and willing to travel.

[Rolls]

Lol guys this is just a thought experiement.

Seriously though it would work the same way a normal supercharger works except in reverse. Instead of forcing air into the engine it would create negative exhaust back pressure causing massive scavenging which would increase VE and cause more air to get into the cylinder. You would put it post turbo, eg after it so it would suck exhaust out, would probably help with spool but mainly at higher load where backpressure is high improving top end.

Being as it is a thought experiement I'd just assume it was powerful enough to suck the gas our and create negative backpressure, eg it wasn't a restriction. I'm not the first one to come up with this idea, do some googling there are quite a few discussions on the same idea.

I think the main reason it would fail is it has to suck out fuel AND air, where as a charger has to only push air normally. Has to move more than twice the volume of gas so would require far more energy. Still fun to think about things like this, keeps your brain working you negative nancys.

As for solving back pressure issues, well you can run a 5 inch pipe and end up with zero...

Or you could use this and get negative backpressure, that was the point, get it below zero.

Your just doing the work twice with that setup aren't you? i mean the piston itself pushing up on the exhaust stroke is just a big pump pumping the gasses out of the chamber.

No you'd be assisting the exhaust stroke by sucking the exhaust out, this would aid in cylinder filling and get more air into the engine.

Superchargers given mechanically driven = off the motor. How do you intend to get the belts behind the exhaust manifold area?

That is just an engineering problem, you could use a shaft from the front area that runs to the end of the exhaust sucker.

lol.

I can't believe some of the questions that get asked here, and then we get told not to flame.

Mafia you are probably the most negative person I have ever met, I've never seen anyone else post such negative bullshit in threads.

Edited September 6, 2011 by Rolls

[blk94r33]

Not quite sure how to word it, but...

Rolls, people are negative, such is life. I honestly though I came up with the idea for sequential turbo's, posted, and of course it'd already been done. You can only learn from asking, and some are better less negative/harsh teachers than others. I've asked much stupider things and learnt from my mistakes, but am better off/smarter from doing so.

I thought up an idea a while ago of a large tank (say 5 litres) hidden somewhere that stores vacuum under idle/cruise etc, then switches a solenoid at WOT to lower the dump/front pipe pressures for a split second to try help spool a turbo quicker. Don't know if it'd work, but thought it was interesting...